Ball screw

ABSTRACT

Ball screw having a spindle nut arranged on a spindle, balls arranged to roll in a thread path being formed by a first thread groove on the spindle and a second thread groove in the spindle nut. At least one deflecting piece arranged in a receptacle in the spindle nut, the piece including a deflecting channel for the return of the balls respectively form a run-out end to a run-in end of at least one common turn of the thread path. The deflecting piece is comprised of two partial deflecting pieces, wherein a parting plane divides the deflecting channel longitudinally, and the partial deflecting pieces are symmetric and have lock together hooks at their circumferential ends.

FIELD OF THE INVENTION

The present invention relates to a ball screw.

DE 199 44 875 A1, for example, discloses a ball screw with a spindle anda nut surrounding the latter, and also with balls arranged in between,which are arranged in such a way that they can roll in a thread grooveformed on the outer surface of the spindle and in a corresponding threadgroove formed on the inner surface of the nut. Also provided on the nutare radial through-openings, in which deflecting pieces are fitted forthe return of the balls respectively from a run-out end of a common turnof the thread grooves to a run-in end of this turn. The nut isconfigured as a one-piece sleeve with a circular-cylindrical casing andeach fitted deflecting piece is arranged in the associatedthrough-opening of the nut completely within the outer casing. Seen incross section, the deflecting pieces are formed in an approximatelyU-shaped manner and have a base and two side plates adjoining the base.Formed between these side plates is a deflecting channel or a deflectinggroove for the return of the balls. The deflecting pieces may beproduced for example from plastic by the injection-molding process. Thedeflecting pieces may be given a spatially complicated form, which isintended to assist satisfactory deflection of the balls. The shaping ofthe deflecting pieces is subject to limits however. This is so because,if the deflecting piece is to be produced for example from plastic bythe injection-molding process, it is not possible for shaping to takeany form desired. For example, in the case of spatially very complicatedshapings, problems may occur with the opening of the injection moldingtool because of undercuts. Or very sophisticated slide molds arerequired, increasing the production costs for such deflecting pieces insuch a way as to make their use problematical from a commercial aspect.

The object of the present invention is to provide a ball screw accordingto the features of the preamble of claim 1 in which the deflecting piececan be produced in a simple manner.

According to the invention, this object is achieved by the deflectingpiece being composed of two partial deflecting pieces, a parting planedividing the deflecting channel longitudinally. In the case of the ballscrew according to the invention, complicated shapings of the deflectingpieces can take place without sophisticated injection molding toolsbeing required. Even complicated spatial shapings which in theproduction of known one-part deflecting pieces necessitate pronouncedundercuts, and consequently require sophisticated slide molds, arepossible. The two partial deflecting pieces can be molded in oneoperation in a common injection molding tool. There is no longer anyneed for sophisticated undercuts or complicated slide molds. The twopartial deflecting pieces merely need to be joined together and thenthey form the deflecting piece.

In the case of the customary individual deflection, a number of completerows of balls which respectively extend over one turn are provided inthe spindle nut. In this case, the deflecting piece reaches over thisone turn.

However, complete rows of balls which extend over more than one turn,for example two turns, may also be provided. In this case, thedeflecting piece reaches over two turns, the run-in end being formed onthe side of the first turn and the run-out end being provided on theside of the second turn. Normally, individual deflections are alsocustomary because it is only in this way that the forces acting in therespective rows of balls on account of the deflecting operation remainbelow a critical value. Above the critical value, undesired runningnoises or operational disruptions may occur because of jamming of theballs.

With the invention, on the other hand, the ball guiding surfaces on thedeflecting pieces may be formed in such a way that the lifting of theballs out of the thread groove of the spindle takes place smoothly andwith low forces. For this reason, the invention is also suitable forball screws with rows of balls which extend for example over two turns.

The one side plate may be formed in one piece on the one partialdeflecting piece and the other side plate may be formed in one piece onthe other deflecting piece. The one partial deflecting piece may thenhave one part of the base and the other partial deflecting piece mayhave another part of the base, it being possible for the two parts ofthe base to complement one another to form the complete base of thedeflecting channel of the deflecting piece.

In a particularly favorable way, the two partial deflecting pieces maybe captively connected to one another, in particular by a film hinge. Inthis way there is no longer any need for sophisticated sorting ofmatching partial deflecting pieces. If a film hinge is to be provided,it can be provided in one operation with the production of the partialdeflecting pieces. The film hinge is then preferably connected in onepiece to both partial deflecting pieces. In this case, there is alreadysatisfactory alignment of the two partial deflecting pieces in relationto one another. The two partial deflecting pieces then merely need to befolded together, the film hinge permitting a folding angle of 180°, sothat the one partial deflecting piece can be folded for example by 180°until it fits onto the other partial deflecting piece. For simpleproduction, and also for simple assembly of the deflecting pieces, itmay be expedient for the two partial deflecting pieces to be formedpoint-symmetrically in a sectional plane arranged transversely to theparting plane, with respect to a point of symmetry lying in the partingplane. On account of the symmetry, there is no need for specialorientation for installation of the deflecting pieces in the spindlenut.

Both side plates of the deflecting piece may be respectively provided attheir free end, facing the thread groove of the spindle, with a bladefor engagement between the ball and the thread groove of the threadedspindle, so that the effective forces during the deflection of the ballsare reduced. The blades may have spatially demanding contours on thefinished deflecting piece. The clear distance between the two free endsof the side plates may be made to be significantly less than the balldiameter. There are no longer difficulties in injection-molding, sincethe parting plane indeed passes through the deflecting channel,consequently the two partial deflecting pieces can also be produced withsimple injection molding tools.

The two-part configuration of the deflecting piece also permits theformation on the deflecting piece of ball guiding surfaces which engagein the thread groove of the spindle, in order to lift the balls off fromthe thread groove of the spindle. In the case of known deflectingpieces, the blades mentioned further above, or else the ball guidingsurfaces, cannot be produced, or only in an extremely sophisticated way,since the shaping requires demanding tools.

Both partial deflecting pieces may be respectively provided with a hookand with a hook receptacle, a hook and a hook receptacle of each of thetwo partial deflecting pieces being able to hook in one another,gripping one another. These hooks and hook receptacles may in particularbe formed in one piece on the partial deflecting pieces and already beallowed for in the injection molding tool. The two partial deflectingpieces then merely need to be folded together, the respective hooks andhook receptacles hooking in one another or interlocking. The deflectingpieces are then ready to install and also cannot be separated from oneanother any longer without external intervention.

Preferably, the hook is provided at the one circumferential end of eachpartial deflecting piece and the hook receptacle is provided at theopposite, other circumferential end. This formation is suitable inparticular for partial deflecting pieces according to the inventionwhich are point-symmetrical to one another in the way described above.In this case, the two partial deflecting pieces can also be formedidentically with the hooks and hook receptacles formed on them.

The deflecting piece is preferably produced from thermoplastic materialby the injection-molding process.

The invention is explained in more detail below on the basis of anexemplary embodiment that is represented in altogether nine figures, inwhich:

FIG. 1 shows a deflecting piece according to the invention in aperspective representation,

FIG. 2 shows the deflecting piece according to the invention as shown inFIG. 1, folded together,

FIG. 3 shows the deflecting piece according to the invention in anelevation,

FIG. 4 shows a section through the deflecting piece according to theinvention from FIG. 3 along the line IV-IV,

FIG. 5 shows an elevation of the perspective representation of thedeflecting piece according to the invention as shown in FIG. 1,

FIG. 6 shows a further elevation of the perspective representation asshown in FIG. 1,

FIG. 7 shows a section along the line VII—VII in FIG. 6,

FIG. 8 shows a detail of the deflecting piece according to the inventionand

FIG. 9 shows a schematic representation of a ball screw according to theinvention.

The ball screw according to the invention that is depicted in FIG. 9comprises a spindle nut 2, arranged on a spindle 1, and balls 3, whichare merely represented here by dashed lines. The balls 3 can roll on athread path 4. The thread path 4 comprises a thread groove 5 formed onthe spindle 1 and a thread groove 6 formed on the spindle nut 2. Thespindle nut 1 is provided with a number of receptacles 7, arrangeddistributed over the circumference, for receiving deflecting pieces 2.Each deflecting piece comprises a deflecting channel 9 for the return ofthe balls 3 respectively from a run-out end 10 to a run-in end 11 of atleast one common turn 12 of the thread path 4.

FIG. 1 clearly shows that the deflecting piece 8 is formed by twopartial deflecting pieces 13, 14, which are captively connected to oneanother in one piece by means of a film hinge 15. FIG. 5 clearly showsfor example the formation of the film hinge 15. The arrows provided inFIG. 5 show how the two partial deflecting pieces 13, 14 are foldedtogether to form the deflecting piece 8 according to the invention.

FIG. 2 shows the folded-together deflecting piece 8 according to theinvention.

FIG. 3 shows an elevation of the deflecting piece 8 according to theinvention, a parting plane 16 clearly being arranged here, in therepresentation that is shown, in an approximately S-shaped manner alongthe deflecting channel 9 and dividing the detecting piece 8 into twopartial deflecting pieces 13, 14. The parting plane 16 has beenrepresented with a greater line thickness in order to illustrate thepath it follows. The S-shaped path is favorable, since the two partialdeflecting pieces 13, 14 have a parting plane which can simply beprovided in the injection molding tool without excessive undercutsoccurring.

FIG. 4 shows a cross section through the deflecting piece 8 according tothe invention, it being clearly evident here that the film hinge 15 ispivoted by approximately 180° after a folding movement of the twopartial deflecting pieces 13, 14 onto one another. The parting plane 16is arranged in such a way that the two partial deflecting pieces 13, 14can be produced alongside one another in a mold of an injection moldingtool, no undercuts being provided on the two partial deflecting pieces13, 14, or at least only undercuts which can be produced with a simpleinjection molding tool.

The representation in FIG. 6 reveals that the two partial deflectingpieces 13, 14 are formed point-symmetrically with respect to a point ofsymmetry P lying in the parting plane 16, the point of symmetry lying ina sectional plane S arranged transversely on the parting plane 16. Onaccount of the symmetrical arrangement, identical partial deflectingpieces 13, 14 are produced. When the two partial deflecting pieces 13,14 are folded together to form the deflecting piece 8 according to theinvention, there is no need for special orientation for installation inthe receptacle 7 of the spindle nut 2.

FIG. 6 also reveals that the two partial deflecting pieces 13, 14 arerespectively provided with a hook 17 and a hook receptacle 18, a hook 17and a hook receptacle 18 of each of the two partial deflecting pieces13, 14 being able to hook in one another, gripping one another. On bothpartial deflecting pieces 13, 14, the hook 17 is formed in one piece atthe one respective circumferential end and the hook receptacle 18 isformed in one piece at the other, opposite circumferential end.

FIG. 7 clearly shows the formation of the hook 17 and the formation ofthe hook receptacle 18 on the one partial deflecting piece 13. It isevident here that undercuts 19, 20 are provided. These undercuts 19, 20are provided for satisfactory interlocking of the hooks 17 and the hookreceptacles 18. However, these undercuts 19, 20 are such that simpleinjection molding tools or slides can be used. After completion of thetwo partial deflecting pieces 13, 14, a so-called forced demolding isthen carried out, in which the partial deflecting pieces 13, 14 withtheir hook and with their hook receptacle 18 are elastically deformed topermit opening of the injection molding tool.

FIG. 8 shows the two interlocking partial deflecting pieces 13, 14 indetail.

FIG. 4 clearly shows that the deflecting channel 9 is bounded by a base21 and two side plates 22, 23 of the deflecting piece 8, the one sideplate 22 being formed in one piece on the one partial deflecting piece13 and the other side plate 23 being formed in one piece on the otherpartial deflecting piece 14.

FIG. 3 reveals that the clear distance between the two free ends of theside plates 22, 23 is significantly less than the ball diameter. Thisconstriction at the free ends is attributable to blades 24, 25, and ballguiding surfaces, which are formed in one piece on both side plates 22,23, respectively at their free ends facing the spindle 1. These blades24, 25 are provided for engagement between the balls 3 and the threadgroove 5 of the spindle 1.

However, FIG. 4 also reveals that on both partial deflecting pieces 13,14 there are formed ball guiding surfaces 26, 27 which engage in thethread groove 5 of the spindle 1, in order to lift the balls 3 off fromthe thread groove 5 of the spindle 1.

The deflecting piece according to the invention can be produced in acommercially particularly favorable way from thermoplastic material bythe injection-molding process.

List of Designations

-   1 spindle-   2 spindle nut-   3 ball-   4 thread path-   5 thread groove-   6 thread groove-   7 receptacle-   8 deflecting piece-   9 deflecting channel-   10 run-out end-   11 run-in end-   12 turn-   13 partial deflecting piece-   14 partial deflecting piece-   15 film hinge-   16 parting plane-   17 hook-   18 hook receptacle-   19 undercut-   20 undercut-   21 base-   22 sideplate-   23 sideplate-   24 blade-   25 blade-   26 ball guiding surface-   27 ball guiding surface

1. A ball screw comprising: a spindle; a first thread groove formed onthe spindle; a spindle nut arranged on the spindle, a second threadgroove formed in the spindle nut, the first and second thread groovesbeing respectively shaped and positioned to together form a thread path;balls arranged such that they can roll in the thread path; a receptaclein the spindle nut and opening to the spindle; at least one deflectingpiece arranged in the receptacle of the spindle nut, the deflectingpiece including a deflecting channel shaped and directed for returningthe balls in the thread path respectively from a run-out end to a run-inend of at least one common turn of the thread path, the deflecting pieceis comprised of two partial deflecting pieces, and is shaped such that aparting plane divides the deflecting channel longitudinally.
 2. The ballscrew as claimed in claim 1, in which the deflecting channel is definedand bounded by a base and two spaced apart side plates attached to thebase of the deflecting piece, the one of the side plates being formed onthe one partial deflecting piece and the other of the side plates beingformed on the other partial deflecting piece.
 3. The ball screw asclaimed in claim 1, in which the two partial deflecting pieces arecaptively connected to one another.
 4. The ball screw as claimed inclaim 1, wherein the two partial deflecting pieces are formedpoint-symmetrically in a sectional plane arranged transversely to theparting plane, with respect to a point of symmetry lying in the partingplane.
 5. The ball screw as claimed in claim 1, wherein each of the sideplates is provided at its respective free end, facing the thread grooveof the spindle, with a respective blade for engagement between at leastone of the balls the ball and the first thread groove of the spindle. 6.The ball screw as claimed in claim 1, wherein there is a clear distancebetween the two free ends of the side plates that is less than the balldiameter.
 7. The ball screw as claimed in claim 1, further comprisingthe deflecting piece engaging the ball guiding surfaces to lift theballs off the first thread groove of the spindle.
 8. The ball screw asclaimed in claim 1, in which each of the partial deflecting pieces isrespectively provided with a hook and with a hook receptacle, the hookand the hook receptacle of each of the two partial deflecting piecesbeing respectively so placed and shaped that each hook hooks into thehook receptacle of the other deflecting piece so that the deflectingpieces hook in one another and grip one another.
 9. The ball screw asclaimed in claim 6, wherein the hook is provided at one circumferentialend of each partial deflecting piece and the hook receptacle is providedat an opposite, other circumferential end.
 10. The ball screw as claimedin claim 1, wherein each of the deflecting pieces is produced inparticular from thermoplastic material by an injection-molding process.11. The ball screw as claimed in claim 3, wherein the deflecting piecesare connected by a film hinge.